1. Field of Invention
This invention relates generally to generally to methods and apparatus for high voltage cable connectivity, and more particularly to electronic methods for high voltage interlock.
2. Background Art
Electric (EV) or hybrid electric vehicles (HEV), can employ electrical energy for propulsion via an electric drive system that can include a power conversion circuit coupled to an electric machine, such as an electric motor. In this arrangement, the power conversion circuit can controllably transfer power from a power source, such as a high voltage battery, to the motor to drive a load. In many cases, the power conversion circuit is integrated with the vehicle transaxle. However, in other instances the power conversion circuit is physically separated from the transaxle, and the two are electrically coupled by a high voltage cable. In this type of system, proper cable connectivity is essential if the system is to operate as intended. For example, when a vehicle electric drive system includes a three-phase permanent magnet synchronous motor, the cable must be connected so that all three phase currents can flow between the power conversion circuit and the motor. Accordingly, vehicles having a power conversion circuit that is remote from the transaxle typically include some means for detecting an open phase. Traditionally, a mechanical means, such as a physical switch is deployed. For example, a housing can include an integrated interlock switch. When a cable connector is plugged into the housing, the interlock switch status can be changed, for example from open to closed. The change in interlock switch state can then be communicated to a system controller via interlock wires. However, the use of a mechanical switch injects a degree of risk to the system, as mechanical parts can degrade, fail, or otherwise prove unreliable.
To avoid the reliability and cost issues associated with the use of mechanical means, alternative methods for determining cable connectivity have been proposed. By way of example, a solution that compares actual stator currents to estimated stator currents to determine connectivity has been disclosed. However, this method is prone to false alarms when employed during operational modes in which motor torque is small. As a further example, a pulsed current method in which a pulsed current is injected at the d-axis of the motor has been disclosed that can indicate connectivity status during low torque operation without triggering a large number of false alarms. However, this method is plagued with undesirable noise vibration harshness (NVH) problems.